. >> reporter: in virginia, romney's down by just two. with a lot on the line in past debates, romney has done well. >> going against romney is not a fun thing. he has the facts. he drills you, stays, tenacious. >> reporter: and sometimes aggressive. >> the idea that i'm anti-immigrant is repulsive. don't use a term like that. >> reporter: aides admit barack obama in debates can sound like a professorial know it all. >> i understand the broader point that senator clinton has been trying to make over the last several weeks. >> reporter: tonight's format is from 2008. moderator jim lehrer, 90 minutes, no breaks. with possible fireworks. >> i think you'll see both of them be more aggressive than either of their campaigns have predicted because the stakes are pretty high. >> reporter: the content could get even tighter, after tonight's clash. but most here in denver agree, this race could be decided by this debate. live at the university of denver, steve handelsman, news4. >>> and of course, nbc news will bring you live coverage of all three